There is not any risk besides you modified some core file - your modification can be lost in this case.
You can re apply it after upgrade if necessary.

aMember upgrade pack include only files that was changed between your version and latest one
to reduce risk of overwriting your custom changes. Only very few files was changed between 5.05 and 5.07
so go ahead and upgrade. It should be seamless.

In case you face any issue - feel free to contact us in helpdesk ( https://www.amember.com/support ). We will be happy to help with it as soon as possible.